Migraine headaches linked to the weather

A variety of headache triggers are relatively well-known: red wine, chocolate, soft cheese and the beginning of the menstrual cycle. But although weather, especially changes in air pressure, is frequently cited as a headache trigger, the connection has not been shown in a large, well-designed study.

Now researchers have found that high temperatures and low air pressure can indeed trigger migraines but that there doesn't seem to be a clear association between such severe headaches and air pollution.

In a large study published online March 9 in the journal Neurology, researchers from Boston's Beth Israel Deaconess Medical Center and the Harvard School of Public Health decided to explore the role of pollution in headaches, because fine-particulate pollutants cause or complicate other health problems, such as heart attacks, stroke, congestive heart failure and asthma.

The study included 7,054 headache patients of both genders and varying ages and ethnic groups who were seen at the medical center's emergency room between May 2000 and December 2007. Researchers looked at temperature levels, barometric pressure, humidity, fine-particulate matter and other pollutants during the three days before each patient was seen in the ER and for a control day, in which the patient did not report a severe headache.

A rise in temperature was strongly associated with headaches: An increase of 5 degrees Celsius (or 9 degrees Fahrenheit) increased the risk of migraine by 7.4%. Low air pressure, which often precedes storms, played a smaller role.

"This study provides pretty rigorous scientific proof that changes in temperature are migraine triggers, and that's something that's not been known before," said Dr. Richard Lipton of the Montefiore Headache Center in New York City.

Knowing what triggers an attack gives migraine sufferers a measure of control, said Lipton, who was not associated with the study. One of his patients, for example, moved from New York to Arizona because air pressure in the Southwest is less changeable.

Triggers often work in concert. So migraine sufferers could, for example, be especially careful to avoid red wine and chocolate on hotter days or when a storm is forecast.

Lipton was less convinced by the study's finding on ambient air pollution, which, he said, was harder than temperature to measure over a large region. But he also said that a similar study that found a correlation between particulate matter and asthma also used a central monitoring site.

The migraine study did find a borderline association between headaches and levels of nitrogen dioxide, found in smog and car exhaust. Given the role of fine-particulate matter in cardiovascular disease, the researchers called for additional study on this.